Device for controlling the contactors of an electric motor



3 Sheets-Sheet 1 N ENToRs ERR? Rwuveu- JEA N'WER'RE ukmER I M s a P.RIONDEL ETAL N I, Q t w 7 0 um ,mH m 6-61mi m A S S Q 0: b .1 G km Jo Jom. i E N Sept. 26, 1967 DE ICE FOR CONTROLLING THE CONTACTORS OF ANELECTRIC MQTOR Filed June 15, 1966 I Sept. 26, 1967 P. RIONDEL ETALDEVICE FOR CONTROLLING THE CONTAGTORS OF AN ELECTRIC MOTOR Filed June15, 1966 3 Sheets-Sheet 2 V m, V V m VP F s ib. 1 .n Fla... PAL +& P r wv v e U1 4 rm 0 MA fiMm rll IIL m n 3 A ar U U i521-) P HUT m U; n H VVW v u 0. F

vzuroR6 PIERRE RIONDEL M I JIM N-WH'JLE (MW/2R United States PatentDEVICE FOR CONTRQLLING THE CGNTACTORS OF AN ELECTRIC MOTOR PierreRiondel and J can-Pierre Garnier, Geneva, Switzerland, assignors toSociete Anonyrne des Ateliers dc Secheron, Geneva, Switzerland FiledJune 15, 1966, Ser. No. 557,697 4 Claims. (Cl. 318-393) The presentinvention relates to means for controlling the electropneumatic orelectromagnetic rheostat contactors of an electric collector motor,which may be a traction motor or a rolling-mill motor.

The present application is a continuation-in-part of our co-pendingapplication Serial Number 437,253, filed March 4, 1965, and nowabandoned, which latter is a continuation-in-part of our abandonedapplication Serial Number 240,387, filed November 27, 1962.

Public transport enterprises using electric traction vehicles aspresently known are characterized by high maintenance cost. For thispurpose, it is desirable to replace conventional mechanically actuatedcontacts by electronic circuits, especially in those cases wherefrequency of operation is high.

For example, in the case of a trolley-bus having a series-wound motorand a starting rheostat, rheostat variations are carried out bycontactors which are successively connected in a given order so as toreduce progressively the resistance of the rheostat as the speed of thetrolleybus increases.

In order to have satisfactory control of the starting current and tolessen the jolts during starting, a relatively great number ofcontactors must be installed. Moreover, traffic conditions such as shorttrips, frequent starts and numerous accelerations and decelerationsbetween successive stops, require the contactors to be subjected tointensive work. These factors cause the contacts used in the controlcircuits of the contactors to be rapidly worn out.

It is an object of the present invention to eliminate this inconvenienceby replacing these mechanical control con tacts with electroniccircuits.

The use of electronics has the additional advantage of facilitatingautomatic control by reducing the power required by the metering andcontrol elements. This allows, for instance, an acceleration regulationto be achieved which is particularly advantageous for runningtrolley-'busses which are required to start and stop under a widevariety of loads and operating conditions, and also on a wide variety ofgrades. If an automatic device is used which tends to maintain thestarting current constant, acceleration will be quite different,depending upon whether the trolley-bus starts on an upgrade or adowngrade, or empty or filled to capacity. Some starts wouldconsequently be too abrupt and others too slow. By using automaticelectronic means which tend to maintain starting acceleration constant,the vehicle can be operated "ice The attached drawing shows, by way ofexample, an embodiment of the device according to the invention,corresponding to the case of a traction motor or, more specifically, astarting device for a trolley-bus.

FIGURE 1 shows a schematic block diagram indicating the interconnectionsof the various units of Said embodiment.

FIGURE 2 shows schematically and by way of example how thediiferentiator and the integrator can be built up.

FIGURE 3 shows schematically and by way of example how the non-linearelements can be built up.

FIGURE 4 shows a characteristic of the nonlinear elements.

FIGURE 5 shows schematically and by way of example how an element can bebuilt up.

The illustrated device comprises the elements 1 to 8 each of which isbuilt up of well-known basic electrical equipment.

A known differentiator 1 (explained below in detail) receives a voltageU which is a function of (for example is proportional to) the speed ofthe vehicle and forms a current E, according to the equation k being aconstant and t being time. It contains a condenser connectedin seriesbetween its inlet and its outlet. Current E, flows through thecondenser.

A potentiometer 2, working in well known manner as a linear functiongenerator, supplies a current E which is a linear function of theangular position of the drivers pedal.

An element 3, receives a voltage U which is a function of (for exampleis proportional to) the current in the motor, and has such acharacteristic that output current E is first of all zero, then variableand positive along a relatively steep slope for a certain input value ofU;. A characteristic of this type can be obtained in well known mannerwith a Zener diode connected in series (for the unsensitive zone) and arelatively weak resistance (for the slope). This element 3 could also bebuilt up according to FIG. 5. In this case, the amplifier indicated atthe right side of FIG. 3 could be that shown in FIG. 2.

An element 4, constituting an algebraic summator amplifier formingp=E,E,E is provided with a series resistor at the inlet and a feed-backresistor between the outlet and inlet. This principle is also wellknown.

A potentiometer 5, working in well-known manner as a linear functiongenerator, supplies a voltage E, which is a linear function of theangular position at of the drivers pedal.

An integrator 6 of known construction (explained below in detail) formsthe integral of the electrical value p according to the formula U =kfpdt, k being a constant. Furthermore, the voltage U cannot exceed thevoltage E, supplied by element 5. This may be accomplished with a diode.

A non-linear element 7 of well-known type (explained below in detail)supplies the control voltage U of the first contactor C. This element iscomposed of an electronic switch whose actuation is determined by apredetermined point of reference.

The non-linear element 8 is identical with element 7, except only forthe point of reference which differs. It

3 supplies the control voltage U (different from U of a second contactorC There may be one or more series of elements such as 7 and 8, eachsupplying a different voltage for the control of a particular contactor.

The device described herein uses an economic coupling of the contactorsto the starting rheostat between a power supply PS and the motor M,inasmuch as each contactor must operate more than once during the samestart and for this purpose successive switches act on each other.

With respect to contactors C and C contactor C responds to a voltage U,,of one volt for example, whereas contactor C responds to a voltage U oftwo volts. After response of C because of the interaction between thetwo elements 7 and 8, contactor C ceases. For it to respond again, thevoltage U must be increased to three volts, at which time contactor Cacts on another contactor, etc.

FIG. 2 shows schematically how the diiferentiator 1 and the integrator 6can be built up. The unit shown in FIG. 2 is an operational amplifierwith three voltage amplification steps, the first two steps beingdifferential ones. After said three steps, there are provided push-pullpower steps for lowering the exit impedance to the desired level.

This amplifier is attached asymmetrically between one entry (6 or 2 andthe zero point. The other entry is coupled to the zero point by means ofan external equilibrium resistance. The exit signals S and S aresymmetrical and in phase opposition. Moreover, S is in phase oppositionwith c and S is in phase opposition with e Such an amplifier, which isknown per se, can be used in known manner for proportional response (P),proportionaldifferential response (PD), proportional-integral response(PI) or proportonal-integral-diiferential response (PID). Those skilledin the art will understand that the amplifier shown in FIG. 2 can beused as calculating element, e.g. for addition, inversion,multiplication by a constant, integration and differentiation withrespect to time. According to the embodiment shown in FIG. 1, theamplifier of FIG. 2 is used in two different ways, namely asdifferentiator 1 and as integrator 6. In the latter case, S is coupledto e over a feedback resistance (not shown).

FIG. 3 shOWs schematically how the non-linear elements 7 and 8 can bebuilt. These elements may comprise a Schmitt-trigger, an amplifier suchas according to FIG. 2, and phase reverse step, and two exit steps. Sucha unit or non-linear element gives an impulse signal when the polarityof the signal between entries e and 2 changes. One of the exit stepsgives a positive signal 8+ and the other exit step gives a negativesignal S..

The entry e /e has differential character, which means that the switcheffect occurs at the moment when the potential difference between e andc changes its sign. However, entries e and c are not entirely symmetric,and it is recommended to use e as signal entry and e as entry for thereference potential. The latter is Zero if e is connected to thezero-point (mass, ground). In this case, a very weak potential put toentry 2 is sufficient to start the switch operation.

FIG. 4 shows a characteristic of such a device for nonlinear elements 7and 8, and it can be seen that the circuit has a hysteresis of Ara mv.,which defines the sensibility of the circuit.

It should be noted that units such as that illustrated in FIG. 3 arewell known in the art.

The device described operates as follows:

When the driver depresses the trolley-bus accelerator, the summator 4 issupplied with a voltage E proportional to the angular position of thepedal. Derivative E, being zero, and the speed of the vehicle also beingzero, it follows that p=E The voltage U increases and element 7 commandscontactor C to respond. At this time, the

current is established in the traction motor and a torque is transmittedto the axle. The vehicle thus starts up with a certain acceleration. Thevalue of p=E,-E diminishes since E +0 and the voltage U increases lessrapidly. Element 8 then commands contactor C to respond. The current inthe traction motor increases, and the axle torque as well as theacceleration ofthe vehicle increases in turn, provoking a progressivelyweaker increase in the voltage U per unit At.

During starts with heavy loads and up steep grades, the current must berelatively great. As the maximum current value permissible in thetraction motor should not be exceeded, element 2 intervenes to preventsuch. The voltage E increases rapidly, in proximity to the maximumpermissible current, and the value of p=E,,E becomes becomes zero, whichprevents the voltage U from going up and thus maintains the notchattained.

The voltage U cannot exceed reference value E, which results in limitingthe number of contacts as a function of the position of the driverspedal.

When the driver releases the pedal, the voltage U being limited by 13,,instantly follows the latter, provoking a regression along contactswhich is proportional to the variation of E,.

The device has been described for the case of acceleration (starting).It is understood that for deceleration (electric braking, the collectormotor then working as a generator) the principle remains the same. 7

It can be seen from the described example that, in principle, the devicecomprises a member producing a variable voltage U and a series ofelectronic switches controlled by this voltage, these switchescontrolling the contactors and being adjusted to act under the effect ofvariable voltages.

In the described example, the member forming the variable voltage U, isautomatic. There could also be such a member, which would be actuated bythe person operating the vehicle as a function of the speed of thevehicle and the intensity of the motors working current, which theoperator can observe in the indicating devices on the dashboard.

The invention is not limited to the case of electric traction motors,but can be applied to other uses such as rolling mill motors.

What we claim is:

1. A device for controlling the rheostat contactors controlling thevoltage fed to an electric collector motor suitable to power a vehicle,comprising means for producing a variable voltage related at least tothe revolution speed of an axis driven by said motor, and a series ofelectronic switches controlled by said voltage, each of said switchescont-rolling one of the contactors and being adjusted to act under theeffect of a different voltage to provide substantially constantacceleration and deceleration of said axis, said means for producing avariable voltage including a first element supplying a voltage dependentupon the position of a vehicle control member, a second elementsupplying a voltage related to the working current of the motor, and anintegrator controlled by the voltages produced by the two aforesaidelements, to maintain its output voltage constant for as long as thework cunrent is greater than a predetermined value and to limit itsoutput voltage to a value proportional to the voltage supplied by thefirst of these elements.

2. A device according to claim 1, wherein the aforesaid means forproducing a variable voltage further includes a third element producinga voltage related to the acceleration of the vehicle, an algebraicsummator forming a voltage representing the difference in the voltagessupplied by the aforesaid third and second elements, the voltagedifference thus formed acting on the integrator.

3. A device according to claim 2, wherein the variable voltage producingmeans further includes a fourth element producing a voltage related tothe position of the aforesaid 5 6 control member, this voltage acting onsaid algebraic References Cited summator in such a way that theacceleration of the UNITED STATES PATENTS :leirinceerls a function ofthe posltlon of this control 2,452,127 10/1948 James X 3 012178 12/1961Barrett 31842O X 4. A devlce according to claim 1, wherein the outlet 5of one switch is connected to the inlet of the preceding 3250944 5/1966Muslck et a1 318422 switch to alter the response value of the latter toenable I each switch to work under a difierent voltage according ORISRADER Prlma'y Examiner to the operating state of the other switches. G.SIMMONS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,344,333 September 26, 1967 Pierre Riondel et a1,

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

In the heading to the printed specification, after line 7, insert Claimspriority, application Switzerland, Nov. 27, 1961 13768/61 Signed andsealed this 8th day of October 1968.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

1. A DEVICE FOR CONTROLLING THE RHEOSTAT CONTACTORS CONTROLLING THEVOLTAGE FED TO AN ELECTRIC COLLECTOR MOTOR SUITABLE TO POWER A VEHICLE,COMPRISING MEANS FOR PRODUCING A VARIABLE VOLTAGE RELATED AT LEAST TOTHE REVOLUTION SPEED OF AN AXIS DRIVEN BY SAID MOTOR, AND A SERIES OFELECTRONIC SWITCHES CONTROLLED BY SAID VOLTAGE, EACH OF SAID SWITCHESCONTROLLING ONE OF THE CONTACTORS AND BEING ADJUSTED TO ACT UNDER THEEFFECT OF A DIFFERENT VOLTAGE TO PROVIDE SUBSTANTIALLY CONSTANTACCELERATION AND DECELERATION OF SAID AXIS, SAID MEANS FOR PRODUCING AVARIABLE VOLTAGE INCLUDING A FIRST ELEMENT SUPPLYING A VOLTAGE DEPENDENTUPON THE POSITION OF A VEHICLE CONTROL MEMBER, A SECOND ELEMENTSUPPLYING A VOLTAGE RELATED TO THE WORKING CURRENT OF THE MOTOR, AND ANINTEGRATOR CONTROLLED BY THE VOLTAGES PRODUCED BY THE TWO AFORESAIDELEMENTS, TO MAINTAIN ITS OUTPUT VOLTAGE CONSTANT FOR AS LONG AS THEWORK CURRENT IS GREATER THAN A PREDETERMINED VALUE AND TO LIMIT ITSOUTPUT VOLTAGE TO A VALUE PROPORTIONAL TO THE VOLTAGE SUPPLIED BY THEFIRST OF THESE ELEMENTS.